#include<stdio.h>

int main()
{
    int n, i;
    double temp, sum=0, mom=1, son=2;
    scanf("%d",&n);
    for (i = 0;i<n;i++)
    {
        sum += son/mom;
        temp = mom;
        mom = son;
        son = son + temp;
    }
    printf("%.2f",sum);

    return 0;
}